Ignition adapters are typically used to adapt the spark plug firing patterns in a DIS four stroke engine to a voltage waveform for display on an oscilloscope. The voltage waveform is then used for diagnostic testing of the ignition system in the engine. In the DIS four stroke engine, the engine has a series of double-ended coils, where each coil fires two spark plugs simultaneously. Each coil is coupled through an ignition module to a timing circuit, which is generally included within an on-board computer. The timing circuit, through the ignition module, provides a voltage spike in the coil. When the voltage through the coil rises, a first spark plug fires on a compression stroke and ignites an air/fuel mixture in a first cylinder, while a second spark plug fires on an exhaust stroke but does not ignite an air/fuel mixture in a second cylinder.
Conventional diagnostic oscilloscopes are designed to display voltage waveforms for conventional four stroke engines, which sequentially fire a series of spark plugs. However, conventional oscilloscopes do not provide the proper waveform for DIS four stroke engines in part because of the above-mentioned design of the double-ended coils. Accordingly, conventional oscilloscopes must be modified, for example with an ignition adapter, to provide a proper voltage waveform for DIS four stroke engines.
The ignition adapter may comprise for example, an electronic circuit inserted between an on-board computer and the leads to the spark plugs, as shown in Friedline et.al. U.S. Pat. No. 4,644,284. The electronic circuit in Friedline is adapted to generate modified timing signals based on commands from an engine analyzer to fire the spark plugs. Friedline shows secondary signals from the #1, #3 and #5 spark plugs, and from the #2, #4 and #6 spark plugs separately received in the circuit, and converted to a voltage waveform for display on an engine analyzer. The circuit monitors the exhaust and compression stroke firings from the #1 spark plug in a first, inductive pickup, and monitors the compression stroke firings in the #1, #3 and #5 spark plugs in a second pickup. The signals are combined and trigger the engine analyzer on the firing of the spark plug during the compression stroke.
Additionally, Sniegowski et al U.S. Pat. No. 4,847,563 discloses a relatively complicated method of providing a conventional voltage waveform on an engine analyzer. A series of six pickups are attached to the spark plug leads to measure the spark plug firing patterns. Sniegowski initially determines the firing sequence for all cylinders and their corresponding signal polarities using a microprocessor. The spark plug leads are sorted depending on their polarity into a first group having negative waveforms, and a second group having positive waveforms. The first group signals are applied through a secondary output for display on an engine analyzer, while the second group signals are inverted before being displayed.
The Sniegowski circuit is triggered by a seventh inductive pickup placed around the #1 spark plug lead from the engine. The microprocessor is triggered during both the compression stroke and the exhaust stroke. The microprocessor divides by two the number of #1 signals generated, and applies the signals to the engine analyzer at the proper time during the secondary waveform parade.
The prior art ignition adapters attempt to provide conventional firing patterns for DIS engine diagnostic testing. However, the prior art circuits can require complicated electronics and many do not allow for flexible control of the trigger level to compensate for variable voltage levels in the circuit. Moreover, the prior art circuits can require cumbersome hookup procedures and significant expense in purchasing and maintaining the diagnostic equipment.